1. Field of the Invention
This invention relates to an apparatus and method of monitoring the battery of an automotive vehicle, or in particular a battery monitor apparatus and method for automobiles and other vehicles capable of detecting the need of change and the degeneration of the battery with a simple configuration.
2. Description of the Related Art
Conventionally, vehicles, or typically, automotive vehicles running on the road have three basic factors of operation to be controlled, “run”, “stop” and “turn”. With the recent development of electronic control operation, however, comfort has become a desire of vehicle users, and the present tendency is toward an increased number of items to be controlled in the vehicle. The manual operation of the seat position and slide door open/close operation, for example, are being electrified, and an electrically-operated curtain and a multispeaker surround system have been added as new parts to be controlled.
On the other hand, most of the in-vehicle devices to be controlled in seeking comfort are electric devices using an in-vehicle battery, and therefore, the battery for supplying power to these electric devices has come to play an important role in the vehicle. A lead storage battery is mainly used as the in-vehicle battery, and supplies power to electric devices, and is charged by an alternator which generates power by the rotation of the vehicle engine.
Although the in-vehicle battery is charged and discharged repeatedly, excessive discharge may lead to battery degeneration, and therefore, in order to prevent degeneration, the battery is controlled optimally in accordance with the battery state (battery charging rate). After a vehicle is left parked, for example, the battery may be discharged (exhausted) by the standby current (dark current) of the electric devices. As a means for preventing the battery exhaustion, a control operation to reduce the discharge is carried out in accordance with the battery charging rate.
If a battery is replaced with another battery of the same size (having the same battery capacitance in a full charged state), then no problems should be encountered. However, in a case where the battery is replaced with a battery of a different size (a battery having a different battery capacity in full charged state), or in the case where the battery is degenerated, the charge control operation or the power cut operation depending on the battery capacitance is required. With regard to the detection of the need for a battery change, Japanese Unexamined Patent Publication No. 2001-297800 discloses a technique comprising a step of detecting when the battery has been changed (hereinafter referred to simply as a battery change), wherein upon detection of a battery change, a new relationship is established between the charge voltage and the current. In this specification, the appended claims and the summary, the battery capacitance is defined as that of a fully charged battery unless otherwise specified.
Also, in the case where the battery is changed, the following methods are employed to determine the battery capacitance after the change:                (1) In the case where a vehicle distributor (dealer) has changed the battery, the capacitance of the replacement battery is overwritten by the dealer in a nonvolatile memory for storing battery capacitance.        (2) Battery capacitance is measured according to battery size using an optical sensor and a battery weight sensor.        
The methods of determining the battery capacitance described above, however, pose the following problems:                In method (1), no means is available for updating the value of the battery capacitance stored in the nonvolatile memory in the case where another person other than the vehicle dealer changes the battery. If the battery is changed by the user, for example, the battery monitor apparatus may erroneously indicate a battery fault (fault alarm).        In method (2), on the other hand, a plurality of sensors are required to detect battery size at an increased cost. Also, the battery state such as increased internal resistance cannot be determined from battery size or weight alone. Although the battery change can be recognized, battery degeneration cannot be detected.        